North Korean dictator Kim Jong-un issued his latest nuclear-program brag Wednesday, saying on state media that his country had developed a nuclear warhead.

According to South Korea’s Yonhap News Agency, Mr. Kim made the remarks at a meeting with scientists and technicians shown on the North’s official TV station.

“It is a very great warhead that is designed in a reasonable structure that enables an instantaneous thermonuclear reaction using our own style of mixed explosives,” Mr. Kim said, according to Yonhap.

He called it a “tremendous” achievement and said the North had realized a “standardized” design, a term that would imply serial production.

North Korea has issued a number of belligerent statements in the past week, including one threat of a pre-emptive nuclear strike against the U.S. homeland, in response to United Nations sanctions and U.S.-South Korean military exercises.

The development of a usable nuclear warhead, if true, would be a major leap forward for North Korea’s nuclear program. There has been widespread skepticism of some of North Korea’s nuclear claims, including what it called a successful test of a hydrogen bomb earlier this year.

Warheads to put on top of missiles are much harder to develop than atomic bombs, which historically came first, at the end of World War II. But warhead-equipped missiles are faster-striking, much more reliable and harder to defend against than bomb-equipped aircraft.

“The nuclear warheads have been standardized to be fit for ballistic missiles by miniaturizing them, [Mr. Kim] noted, adding this can be called true nuclear deterrent,” said a report on the North’s official Korean Central News Agency.